U.S. patent number 6,130,290 [Application Number 09/277,002] was granted by the patent office on 2000-10-10 for impact modifier for amorphous aromatic polyester.
This patent grant is currently assigned to Rohm and Haas Company. Invention is credited to Joseph John Ryan, Edward Joseph Troy.
United States Patent |
6,130,290 |
Troy , et al. |
October 10, 2000 |
Impact modifier for amorphous aromatic polyester
Abstract
Impact modifiers that produce transparent, high Dynatup impact
strength blends with amorphous, aromatic polyesters are described.
The impact modifiers are core-shell polymers with (A) a core
composed principally of rubbery polymers, such as copolymers of
diolefins with vinyl aromatic monomers, such as copolymers of
butadiene with styrene, (B) an intermediate stage composed
principally of hard polymers, such as polymers or copolymers of
vinyl aromatic monomers, and (C) a shell composed principally of
vinyl aromatic copolymers that contain hydroxyl functional groups
or their equivalents (e.g. styrene/hydroxyalkyl (meth)acrylate
copolymers).
Inventors: |
Troy; Edward Joseph (Bristol,
PA), Ryan; Joseph John (Yardley, PA) |
Assignee: |
Rohm and Haas Company
(Philadelphia, PA)
|
Family
ID: |
22178291 |
Appl.
No.: |
09/277,002 |
Filed: |
March 26, 1999 |
Current U.S.
Class: |
525/63; 525/64;
525/67; 525/71; 525/902 |
Current CPC
Class: |
C08F
255/00 (20130101); C08F 257/02 (20130101); C08F
279/02 (20130101); C08F 285/00 (20130101); C08L
51/04 (20130101); C08L 67/02 (20130101); C08L
51/04 (20130101); C08L 67/02 (20130101); C08L
51/00 (20130101); C08F 285/00 (20130101); C08F
212/00 (20130101); C08L 2666/04 (20130101); Y10S
525/902 (20130101) |
Current International
Class: |
C08F
285/00 (20060101); C08L 67/00 (20060101); C08L
67/02 (20060101); C08G 063/48 (); C08G 063/91 ();
C08L 051/08 (); C08L 051/00 (); C08L 053/00 () |
Field of
Search: |
;525/71,902,64,67,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
597275 B1 |
|
Oct 1993 |
|
EP |
|
93/21274 |
|
Oct 1993 |
|
WO |
|
Other References
JP 54-48850 (English Translation), Apr. 1979..
|
Primary Examiner: Niland; Patrick D.
Attorney, Agent or Firm: Rosedale; Jeffrey H.
Parent Case Text
This application claims benefit of Provisional Application Ser. No.
60/083,432 filed Apr. 29, 1998.
Claims
We claim:
1. A core-shell impact modifier composition comprising
(A) from about 15 to about 85 parts of a core comprising from about
40 to about 60 percent by weight of units derived from at least one
vinyl aromatic monomer, from about 20 to about 60 percent by weight
of units derived from at least one 1,3-diene, up to about 10
percent by weight of units derived from at least one
copolymerizable vinyl or vinylidene monomer, and up to about 5
percent by weight of at least one graft-linking or cross-linking
monomer;
(B) from about 10 to about 50 parts of an intermediate stage
comprising at least about 25 percent by weight of units derived
from at least one vinyl aromatic monomer; and
(C) from about 5 to about 35 parts of an outer shell comprising
from about 2 to about 40 percent by weight of units derived from at
least one hydroxyalkyl (meth)acrylate, from about 60 to about 98
percent by weight of units derived from at least one vinyl aromatic
monomer, and up to about 25 percent by weight in the shell of units
derived from one or more copolymerizable vinyl or vinylidene
monomer, and up to about 5 percent by weight of units derived from
at least one graft-linking or cross-linking monomer;
the core-shell impact modifier having a refractive index of from
about 1.55 to about 1.60.
2. The core-shell impact modifier of claim 1 where the core (A)
comprises
(1) from about 10 to about 50 parts based upon the impact modifier
of an inner stage comprising at least 80 percent of units derived
form at least one vinyl aromatic monomer, up to about 20 percent of
units derived from at least one other copolymerizable vinyl or
vinylidene monomer, up to about 20 percent by weight of units
derived from at least one 1,3-diene, and up to about 5 percent by
weight of units derived from at least one graft-linking or
cross-linking monomer; and
(2) from about 5 to about 75 parts based upon the impact modifier
of an outer stage comprising up to about 60 percent by weight of
units derived from a vinyl aromatic monomer, at least about 30
percent by weight of units derived from at least one 1,3-diene, up
to about 10 percent by weight of units derived from at least one
copolymerizable vinyl or vinylidene monomer, and up to about 5
percent by weight of units derived from at least one graft-linking
or cross-linking monomer.
3. The core-shell impact modifier of claim 1 where the outer shell
(C) comprises a plurality of stages.
4. The core-shell impact modifier of claim 1, 2 or 3 where the
vinyl aromatic monomer is selected from styrene, para-methyl
styrene, alpha-methyl styrene, chlorostyrene, vinyl toluene,
bromostyrene, dibromostyrene, tribromostyrene, iso-propenyl
napthalene, or vinyl naphthalene, and where the 1,3-diene is
butadiene.
5. The core-shell impact modifier of claim 1, 2 or 3 where the
hydroxyalkyl (meth)acrylate is selected from hydroxyethyl
(meth)acrylate or hydroxypropyl (meth)acrylate.
6. A clear amorphous blend comprising:
(A) at least one amorphous aromatic polyester or copolyester having
a refractive index of from about 1.55 to about 1.60; and
(B) the composition of claim 1, 2 or 3;
at a weight ratio of about 99/1 to about 70/30.
7. Articles produced from the blend of claim 6 under conditions
that maintain the polyester in an amorphous condition.
Description
BACKGROUND
The present invention relates to an impact modifier composition
which provides an improved balance of impact resistance and optical
clarity to amorphous aromatic polyester resin (hereafter referred
to as polyester). More specifically, the present invention concerns
an impact modifier composition which contains a rubbery core, an
intermediate hard stage, and a shell containing a hydroxyl group or
another functional group which acts in a similar manner as the
hydroxyl group.
Polyesters (e.g., polyethylene terephthalate, polybutylene
terephthalate, etc.) exhibit various excellent properties such as
resistance to temperature, chemicals, weathering, radiation and
burning and also exhibit excellent clarity (in amorphous form),
reasonable cost, as well as moldability. Accordingly, polyesters
are used for various purposes (e.g., fibers, films, molded and
extruded products, etc.). The impact resistance of the polyester,
however, is less than satisfactory. Plastics such as poly (butylene
terephthalate) (PBT) and poly(ethylene terephthalate) (PET) have
insufficient impact strength, and many attempts have been made to
improve the impact strength. Many agents have been proposed to
improve the impact strength. These are added to resins and
subjected to melt-blending.
Various attempts have been made using conventional fibrous
inorganic fillers (e.g., glass fiber, asbestos fiber, etc.) to
improve the impact resistance of polyester. Even when these methods
are implemented, however, the impact resistance improvement is less
than satisfactory and clarity in amorphous polyesters is adversely
affected.
Various techniques wherein rubbery polymers or rubber- containing
polymers are mixed with polyesters have been developed to improve
the impact resistance of polyesters and thermoplastic materials.
Specifically, certain core-shell polymers comprising a core made of
rubbery polymer and a shell, around the core, made of a glassy
polymer are excellent agents for improvement of impact strength of
polyesters where clarity is not an object.
When these prior art methods are used, the polyester resin
generally exhibits poor compatibility with the shell of the
rubber-containing polymer, and therefore impact resistance is not
fully optimized. Even when these prior art core-shell modifiers are
added to amorphous polyesters and found to produce ductile, notched
breaks, the clarity of amorphous polyester resins is destroyed. An
amorphous polyester may contain a small amount of crystallinity,
but the level must be low enough so that clarity is not adversely
affected. Further, although the polyester may be crystallized under
certain conditions, in the present invention the molding and
cooling conditions are such that crystallization (and loss of
clarity) is avoided.
Lane, U.S. Pat. No. 4,034,013 teaches core/shell polymers
functionalized with an epoxy group, such as a shell of methyl
methacrylate/glycidyl methacrylate, to improve the melt strength of
polyesters. Although Lane broadly teaches butadiene-based
elastomers with optional minor amounts of
styrene in the core and teaches styrene as a major component of the
outer stage, she does not teach or suggest a solution to preparing
an efficient impact modifier which will retain clarity in the
amorphous polyester.
Kishimoto et al., Japanese Kokai 54-48850, disclose butadiene-based
core/shell polymers with hydroxyalkyl groups in the shell portion
as modifiers for crystalline polyesters, such as poly(butylene
terephthalate), but do not teach the means to modify such
core/shell polymers to make them useful as impact modifiers in
clear, amorphous polyesters.
Carson et al., U.S. Pat. No. 5,321,056 teaches impact modifiers
which produce transparent, high notched Izod impact strength blends
with amorphous aromatic polyesters. Carson's impact modifiers are
core-shell polymers with cores comprised mainly of rubbery polymers
of diolefins and vinyl aromatic monomers and shells comprised
mainly of vinyl aromatic monomers and monomers containing a
hydroxyl group. Although Carson provides for significantly improved
impact strength of clear, amorphous aromatic polyester, a need
still exists for a modifier that can provide an improved balance of
properties between impact strength and optical clarity.
Specifically, a need exists to reduce or eliminate the blue/yellow
hue or tint that often results from blending such modifiers in
amorphous aromatic polyester resins.
The object of the present invention is to provide a composition for
improving the impact strength of polyesters, such as PET or PET
copolyesters, when they are processed into clear, tough objects
while retaining their amorphous nature. It is another objective
that said composition provide improved impact properties without
reducing the transparency of amorphous polyesters. A further
objective is that the composition provide reduced blue/yellow hue,
while maintaining desirable impact and transparency
characteristics. Another object is to provide a composition which
will also overcome the embrittlement caused by physical aging which
commonly occurs in amorphous aromatic polyesters when conditioned
at temperatures approaching glass transition temperature (Tg). A
still further object is to provide clear amorphous extrusion/melt
shaped or injection molded PET or PET copolyester articles.
STATEMENT OF INVENTION
In the present invention, impact strength of amorphous aromatic
polyesters is increased substantially by the addition of small
amounts of certain core-shell modifiers which disperse very readily
in aromatic polyesters and do not detract from clarity.
Additionally, the present invention provides an improved balance of
impact resistance and optical properties over previously known
compositions. Specifically, the present invention provides impact
modifiers that substantially reduce the blue/yellow hue of
impact-modified clear amorphous aromatic polyesters. These and
other objects as will become apparent from the following disclosure
are achieved by the present invention.
The impact modifier composition of this invention is a core-shell
polymer with (A) a rubbery core such as a copolymer containing a
diolefin, preferably a 1,3-diene, (B) an intermediate stage
comprised mainly of a hard polymer such as a polymer containing a
vinyl aromatic monomer, and (C) a shell comprised mainly of a vinyl
aromatic monomer (such as styrene), and hydroxyalkyl (meth)acrylate
or, in the alternative, another functional monomer which acts in a
manner similar to the hydroxyalkyl (meth)acrylate).
The impact modifier of the present invention comprises:
(A) from about 15 to about 85 parts of a core stage comprising from
about 40 to about 60 percent by weight of units derived from a
vinyl aromatic monomer, from about 20 to about 60 percent by weight
of units derived from at least one 1,3-diene, up to about 10
percent by weight of units derived from at least one
copolymerizable vinyl or vinylidene monomer, and up to about 5
percent by weight of at least one graft-linking or cross-linking
monomer;
(B) from about 10 to about 50 parts of an intermediate stage
comprising at least about 25 percent by weight of units derived
from a vinyl aromatic monomer; and
(C) from about 5 to about 35 parts of an outer shell comprising
from about 2 to about 40 percent by weight of units derived from at
least one hydroxyalkyl (meth)acrylate, from about 60 to about 98
percent by weight of units derived from at least one vinyl aromatic
monomer, and up to about 25 percent by weight in the shell of units
derived from one or more copolymerizable vinyl or vinylidene
monomer, and up to about 5 percent by weight of units derived from
at least one graft-linking or cross-linking monomer.
A further variation of the impact modifier structure is to provide
within the core (A): (1) an inner hard stage and, (2) an outer
rubbery stage. The inner hard stage comprises at least 80 percent
of units derived form at least one vinyl aromatic monomer, up to
about 20 percent of units derived from at least one other
copolymerizable vinyl or vinylidene monomer, up to about 20 percent
by weight of units derived from at least one 1,3-diene, and up to
about 5 percent by weight of units derived from at least one
graft-linking or cross-linking monomer.
The outer rubbery stage comprises up to about 60 percent by weight
of units derived from a vinyl aromatic monomer, at least about 30
percent by weight of units derived from at least one 1,3-diene, up
to about 10 percent by weight of units derived from at least one
compolymerizable vinyl or vinylidene monomer, and up to about 5
percent by weight of units derived from at least one graft-linking
or cross-linking monomer.
As used throughout this document, the term "stage" is intended to
encompass its broadest possible meaning, including the meaning
conveyed in prior art such as U.S. Pat. No. 3,793,402, U.S. Pat.
No. 3,971,835, U.S. Pat. No. 5,534,594, and U.S. Pat. No.
5,599,854, which offer various means for achieving "staged"
polymers.
Another aspect of the invention is the blending of the impact
modifier composition with at least one aromatic polyester and/or
copolyester at a weight ratio of about 99/1 to about 70/30 of
polyester/impact modifier, the polyester remaining amorphous. A
still further aspect of the invention comprises molded parts,
bottles, sheet, films, pipes, foams, containers, profiles, or other
articles prepared in accordance with the above-mentioned
compositions and blends.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that certain core-shell impact modifiers produce
clear, and unexpectedly tough blends with amorphous aromatic
polyesters. These modifiers produce a large increase in impact
strength, while maintaining excellent optical clarity of the
polyesters. These modifiers have (A) a core composed principally of
rubbery polymers, such as copolymers of diolefins with vinyl
aromatic monomers, such as copolymers of butadiene with styrene,
(B) an intermediate stage composed principally of hard polymers,
such as polymers or copolymers of vinyl aromatic monomers, and (C)
a shell composed principally of vinyl aromatic copolymers that
contain hydroxyl functional groups or their equivalents (e.g.
styrene/hydroxyalkyl (meth)acrylate copolymers). For example, the
core-shell impact modifiers (i.e. "modifiers") which give this
unexpected result contain shells derived from copolymers of vinyl
aromatic monomers with certain hydroxyalkyl (meth)acrylates, for
example, hydroxyethyl (meth)acrylate (HEMA), hydroxypropyl
(meth)acrylate (HPMA), 4-hydroxybutyl acrylate, ethyl
alpha-hydroxymethylacrylate, or hydroxyethyl acrylate (HEA), or
other copolymerizable monomers containing one or more hydroxyl
groups, such as allyl cellosolve, allyl carbinol, methylvinyl
carbinol, allyl alcohol, methallyl alcohol, and the like. Also
included are other monomers which function in a similar manner, for
example, glycidyl methacrylate (GMA), 3,4-epoxybutyl acrylate,
acrylonitrile, methacrylonitrile, beta-cyanoethyl methacrylate,
beta-cyanoethyl acrylate, cyanoalkoxyalkyl (meth)acrylates, such as
omega-cyanoethoxyethyl acrylate, or omega-cyanoethoxyethyl
methacrylate, (meth)acrylamides, such as methacrylamide or
acrylamide, N-monoalkyl (meth)acrylamides, such as
N-methylacrylamide or N-t-butylacrylamide or N-ethyl
(meth)acrylamide, or vinyl monomers containing an aromatic ring and
an hydroxyl group, preferably non-phenolic, such as vinylphenol,
para-vinylbenzyl alcohol, meta-vinylphenethyl alcohol, and the
like. Styrene homopolymer and other styrene copolymers and
terpolymers, such as styrene/methyl methacrylate are very much less
effective.
The monomer concentrations in the core, intermediate stage and
shell of the modifier composition are adjusted to provide a
refractive index (RI) to match that of the polyesters with which
they are blended (i.e. about 1.55 to about 1.60). This produces a
clear blend under processing conditions which will maintain the
polyester in its amorphous form. Almost all rubbery polymers (e.g.
cores) have RI's well below this range. Therefore it is necessary
that the rubber phase concentration of the impact modifier
composition be kept relatively low and the other components of the
modifier be used to bring the RI into the desired range. However,
the impact strength obtainable with a given concentration of any
core-shell impact modifier tends to vary directly with the amount
of rubber polymer in the modifier. This means that high RI
modifiers having low rubber contents have to be exceptionally
efficient to produce good toughening.
From a practical standpoint the most desirable monomer to produce
rubbery polymer for this application is butadiene whose homopolymer
has a RI=1.52. It has the best combination of RI, cost, stability,
and processability. For the same reasons, styrene is the most
desirable component for the rest of the modifier. However, even if
butadiene and styrene were the only components of the modifier, a
butadiene/styrene ratio ranging from about 50/50 to 20/80 would be
required for the modifier RI to be in the 1.55 to 1.60 range needed
for matching the RI's of amorphous, aromatic polyesters. One
skilled in the art of impact modification would expect a 50%
concentration of butadiene to be very low for good core-shell
impact modifier efficiency. The results found herein for
modification of polyesters with such functionalized "rubber-poor"
modifiers are surprisingly good.
In response to the need to match RI's of amorphous aromatic
polyesters and simultaneously have excellent impact modifier
efficiency, U.S. Pat. No. 5,321,056 reports that when low
concentrations of certain hydroxyalkyl (meth)acrylates are
copolymerized with aromatic vinyl monomers to form the shell of
core-shell impact modifiers having RI's in the 1.55 to 1.58 range,
very high notched Izod impact strengths are obtained with amorphous
polyesters at 30% or lower modifier loadings, and preferably at
from about 5 to about 20% loadings. Substitution of the
hydroxyalkyl methacrylate with other functional monomers promoting
compatibility of the shell with the polyester will give similar
results in impact improvement and maintenance of clarity. The
modifier composition of the present invention provides improved
optical properties over the polymers reported in U.S. Pat. No.
5,321,056, while maintaining the reported excellent impact modifier
efficiency of the compositions.
The requirement for a "rubber-poor" modifier can be relaxed
somewhat if the vinyl aromatic monomer is changed from styrene,
vinyl toluene, para-methylstyrene, monochlorostyrene and the like
to one of high refractive index, viz., the polybrominated vinyl
aromatics or the polycyclic vinyl aromatics.
The core of the impact modifier composition of the present
invention is a rubbery polymer and generally comprises a copolymer
of butadiene and a vinyl aromatic monomer. The rubbery polymer may
include diene rubber copolymers (e.g., butadiene-styrene copolymer,
butadiene-styrene-(meth)acrylate terpolymers,
butadiene-styrene-acrylonitrile terpolymers, isoprene-styrene
copolymers, etc.). Of the afore-mentioned rubbery polymers, those
which can be produced as a latex are especially desirable. In
particular, a butadiene-vinyl aromatic copolymer latex obtained as
a result of emulsion polymerization is preferred. In the core, a
partially crosslinked polymer can also be employed if crosslinking
is moderate. Further, at least one of a cross- or graft-linking
monomer, otherwise described as a multi-functional unsaturated
monomer, can also be employed. Such monomers include
divinylbenzene, diallyl maleate, butylene glycol diacrylate, allyl
methacrylate, and the like.
The ratio of comonomers in the core depends on the desired
core-shell ratio and hardness of the rubber phase. The ratio range
of butadiene to the vinyl aromatic in the core polymer is 70/30 to
20/80 (parts by weight). If the quantity of butadiene is below 20
parts by weight, it is difficult to improve the impact resistance.
If the quantity of butadiene exceeds 70 parts by weight, on the
other hand, it is difficult to obtain a high enough RI modifier to
match that of the polyester, unless the vinyl aromatic monomer is
of high refractive index and selected from the polybrominated or
polycyclic monomers described above. Optionally, a small
concentration, from about 0.01 up to about 5, and preferably from
about 0.1 up to about 2 percent, by weight of a crosslinking
monomer, such as divinyl benzene or butylene glycol dimethacrylate
is included, and optionally about 0.01 to about 5 percent by weight
of a graftlinking monomer for tying the core and shell together,
such as allyl maleate may be included in the rubbery core polymer.
Further examples of crosslinking monomers include alkanepolyol
polyacrylates or polymethacrylates such as ethylene glycol
diacrylate, ethylene glycol dimethacrylate, butylene glycol
diacrylate, oligoethylene glycol diacrylate, oligoethylene glycol
dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane
dimethacrylate, trimethylolpropane triacrylate or
trimethylolpropane trimethacrylate, and unsaturated carboxylic acid
allyl esters such as allyl acrylate, allyl methacrylate or diallyl
maleate.
As the intermediate stage of the impact modifier composition, hard
polymers or copolymers of vinyl aromatic monomers are preferred.
Generally, polymers or copolymers with a Tg above room temperature
can be used. Examples of suitable vinyl aromatic monomers include
vinyl aromatic monomers such as styrene, alpha-methyl styrene,
para-methyl styrene, chlorostyrene, vinyl toluene, dibromostyrene,
tribromostyrene, vinyl naphthalene, isopropenyl naphthalene,
divinyl benzene and the like.
As the shell of the impact modifier composition, a
hydroxyl-group-containing monomer is preferred to be employed. When
a hydroxyl group is introduced to the shell polymer, a vinyl
monomer containing an active double-bond segment and a hydroxyl
group (hereafter referred to as hydroxyl-group-containing monomer)
is copolymerized with another copolymerizable vinyl monomer.
Examples of the aforementioned hydroxyl-group-containing monomers
include hydroxyalkyl (meth)acrylate or alpha-hydroxymethylacrylate
esters, such as hydroxyethyl (meth)acrylate, hydroxypropyl
(meth)acrylate, or ethyl hydroxymethylacrylate, allyl derivatives
of hydroxyl-group containing compounds, such as allyl cellosolve,
allyl carbinol, methylvinyl carbinol, allyl alcohol, methallyl
alcohol, and the like, vinylphenol, para-vinylbenzyl alcohol,
meta-vinylphenethyl alcohol, and the like.
Although the hydroxyalkyl (meth)acrylate monomers are preferred for
reasons of safety in handling (over the nitrile-containing
monomers) or availability (over other monomers taught herein),
other monomers which function in a similar manner may be employed,
for example, glycidyl methacrylate (GMA), 3,4-epoxybutyl acrylate,
acrylonitrile, methacrylonitrile, beta-cyanoethyl methacrylate,
beta-cyanoethyl acrylate, cyanoalkoxyalkyl (meth)acrylates, such as
omega-cyanoethoxyethyl acrylate, or omega-cyanoethoxyethyl
methacrylate, (meth)acrylamide, or N-monoalkyl (meth)acrylamide and
the like.
Vinyl aromatic monomers to be copolymerized with the aforementioned
hydroxyl-group-containing monomers include vinyl aromatic monomers
such as styrene, alpha-methyl styrene, para-methyl styrene,
chlorostyrene, vinyl toluene, dibromostyrene, tribromostyrene,
vinyl naphthalene, isopropenyl naphthalene, and the like. The
hydroxyl-group-containing monomers and vinyl aromatic monomers may
be used either singly or in combination of two or more.
In the shell, the ratio between the hydroxyl- group-containing
monomer (e.g. HEMA, HPMA) or a monomer which performs in a similar
manner (e.g. MAN, AN, or GMA), and the other copolymerizable vinyl
monomers (e.g.
styrene, tribromostyrene) ranges from 2/98 to 40/60 parts by
weight, and preferably 3/97 to 30/70 parts by weight. Below 2
parts, the performance is not improved over the vinyl aromatic
homopolymer shell, and above that level, side reactions, such as
crosslinking, may occur, with adverse effects on dispersion.
Optionally, one or more additional monomers may be added to the
shell to adjust the RI. This additional monomer is preferably an
alkyl (meth)acrylate (such as C.sub.1 -C.sub.4 alkyl (meth)
acrylate, and the like), but it can be any monomer which
copolymerizes with the other two monomers used in the core polymer
and produces a terpolymer which permits the RI of the modifier to
match that of the polyesters with which it is blended.
The additional monomer may include one or more of any of the
following monomers: acrylonitrile, methacrylonitrile, methyl
acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,
2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl
methacrylate, divinyl benzene and the like.
The resultant composition preferably has a particle size range of
about 75 to about 300 nm, more preferably from about 140 nm to
about 230 nm, and a RI range of about 1.55 to about 1.60.
When the impact modifier composition containing 15-85 parts by
weight of the aforementioned rubbery core, 10-50 parts by weight of
the intermediate stage, and 5-35 parts by weight of the shell
hydroxyl-group-containing polymer (total: 100 parts by weight) is
manufactured, conventional methods for manufacturing ordinary
rubber-modified polymers (e.g., ABS resin, impact resistant
polystyrene, etc.) may be effectively employed. These impact
modifiers may be prepared by emulsion polymerization. The preferred
procedure is emulsion polymerization using soaps, initiators and
processing conditions normally used for making MBS polymers, that
is, impact modifiers based on butadiene-styrene rubbers with one or
more stages of styrene or methyl methacrylate polymers. Isolation
from the emulsion can be achieved by standard procedures such as
spray drying or coagulation. For example, a polymer latex
characterized by an appropriate particle size and degree of
conversion is produced by means of emulsion polymerization (e.g.
copolymerizing a hydroxyl-group-containing monomer with another
copolymerizable vinyl monomer in the presence of a polymerized
rubber latex upon which a vinyl aromatic monomer has been
polymerized or copolymerized to form an intermediate hard
stage).
Further, the polymer can be prepared by a method wherein a core is
uniformly graft-polymerized with an intermediate hard stage
comprising at least one vinyl aromatic monomer, which is uniformly
graft-polymerized with a hydroxyl-group-containing monomer and
another copolymerizable vinyl monomer constituting the shell
polymer.
Thus, when the impact modifier composition is manufactured, general
free radical polymerization techniques (e.g., emulsion
polymerization, solution polymerization, and suspension
polymerization) may be employed so long as the resulting impact
modifier composition is characterized by a core-shell structure
wherein hydroxyl groups are preserved.
The impact modifier composition may be isolated from the reaction
medium by any of several known processes. For example, when
prepared in emulsion, the composition may be isolated by
coagulation, including coagulation in an extruder from which the
water is removed as a liquid, or by spray-drying. Additives such as
thermal stabilizers and anti-oxidants may be added to the
composition prior to, during or after, isolation.
It is important that no crystallization promoter is present in the
composition since this invention is directed to compositions
suitable for producing amorphous, non-crystalline articles. If
substantial crystallization occurs in the process, the resultant
articles become opaque and brittle. In some cases, such as with
pipe, foam and profile extrusion, a small degree of crystallinity
may be acceptable and can be achieved by control of the cooling
cycle. However, in most cases it is preferred to prepare amorphous
articles on standard injection molding and extrusion equipment. The
type of articles to be produced, whether it be molded parts,
bottles, films, foams, pipes, tubing, sheet or profiles, will
govern the auxiliary equipment to be employed. For instance, to
produce bottles, extrusion blow molding equipment is necessary. To
produce film, blown film equipment is necessary.
The amorphous, aromatic polyesters, such as PET, and copolyesters,
such as Eastman PETG (i.e.,
(poly)ethylene-co-1,4-cyclohexanedimethylene terephthalate), of
this invention include poly (C.sub.1 to C.sub.6 alkylene
terephthalates), alkylene naphthalene dicarboxylates, such as
poly(ethylene naphthalene-2,6-dicarboxylate), and aromatic
amorphous polyester which contains units derived from at least one
aliphatic diol or cycloaliphatic diol or combinations of aliphatic
diols and cycloaliphatic diols and one or more aromatic dibasic
acids. Examples include polyethylene terephthalate (PET),
polypentylene terephthalate, and the like, or an aromatic
copolyester which contains units derived from two glycols (e.g.,
ethylene glycol, and cyclohexanedimethanol) or from two dibasic
acids (e.g. terephthalic acid and isophthalic acid). Such
polyesters may be obtained by polycondensing polyol components
(e.g., ethylene glycol) with dicarboxylic acid components (e.g.,
terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid,
etc.), as well as mixtures consisting of two or more
polyesters.
The modifiers and polyesters may be combined by melt blending in an
extruder. The polyesters should be dried to 0.03% moisture content.
A mix of the two components can be directly extruded or molded or
the components can be combined in an initial blending step and the
pellets from this blend can then be molded after drying to a 0.03%
moisture content. The concentration of modifier in these polyester
blends can range from about 1 to about 30% by weight and preferably
from about 5 to about 20% by weight. The blends can be extruded or
molded into clear parts which have very high Dynatup impact
strength, and exhibit ductile type failures and physical aging
resistance. The required modifier concentration will depend on
factors such as the molecular weight of the polyester, the impact
strength desired, and the temperature at which the final object is
utilized. Below 1% modifier concentration, no significant effect is
seen.
Blends should contain amorphous aromatic polyester or copolyester
which has an intrinsic viscosity of greater than or equal to 0.7
dl/g. for best properties of molding and processing, but for some
uses, lower molecular weight polyesters may be employed. (PET or
PETG may decrease in intrinsic viscosity after melt processing; the
values in the specification refer to the polyester as supplied,
prior to processing). Articles such as containers, bottles, foam,
or hollow parts may be extrusion blow molded, extruded or injection
molded from polyester blends described herein.
Blending can be accomplished by melt extrusion in an extruder at
temperatures of about 193.degree. C. to about 288.degree. C.,
preferably about 204.degree. C. to about 265.degree. C. For
example, a high work, two stage screw which has a length/diameter
ratio of about 24/1, and a compression ratio of about 3.0 to 3.5
gives a very adequate dispersion of the modifier in the polyester.
A dwell time in the extruder of 1 to 5 minutes is adequate to
insure complete mixing or dispersion under most conditions but of
course lower and higher dwell times can certainly be used.
Preferably the strands produced by extruder blending are pelletized
and dried to a moisture content of less than 0.03 percent before
molding.
The ingredients used to make the composition of the invention are
dispersed uniformly and it has been found that melt blending the
ingredients, by using such equipment as a melt extruder (e.g.,
single screw extruders or twin screw extruders) in a separate step
prior to molding is desirable. The blended product may be
pelletized (i.e., the extruded strand is quenched and cut), dried
and used for subsequent molding purposes.
Other additives known in the art may be included in the composition
at about 1 to about 30% by weight. These other additives may
include antioxidants, flame retardants, reinforcing agents such as
glass fiber, asbestos fiber and flake, mineral fillers,
stabilizers, nucleating agents, ultraviolet light stabilizers, heat
and light stabilizers, lubricants, dyes, pigments, toners, mold
release agents, fillers, such as glass beads and talc, and the
like. Minor amounts of other polymers (i.e. about 1 to about 10
percent by weight) can also be incorporated in the present
composition, such as polyamides or polycarbonates. Most of these
additives will adversely affect clarity. The additives listed above
such as antioxidants, thermal stabilizers, fillers, pigments and
flame retardant additives may be used in the composition of this
invention provided they do not exert any adverse effect on the
impact strength or clarity. It is preferred not to have glass fiber
reinforcement in clear article applications or any additive which
would decrease transparency. It is highly preferred that clear
articles are produced.
The polyesters must be thoroughly dried prior to melt processing to
minimize the rapid hydrolytic degradation known to occur at
processing temperatures and to reduce molecular weight. The
modifiers of the present invention are much less sensitive to
hydrolytic degradation than the polyesters. Higher than necessary
melt temperatures should be avoided during processing to keep the
impact strength as high as possible. Melt cooling should be carried
out as rapidly as possible to prevent polyester crystallization and
the loss of clarity.
Aromatic amorphous polyesters are quite sensitive to embrittlement
from physical aging, but this limitation is overcome by the
modifiers herein (see Table 1). Therefore, polyester blends will
now be able to compete successfully with polycarbonate,
cellulosics, impact modified polyvinyl chloride, and the like for a
broad range of applications where high clarity and toughness are
needed in the absence of exceptional heat resistance.
The preferred poly(alkylene terephthalates) are polyethylene
terephthalate (PET) and copolyesters of PET. Blends with other
polyesters are also suitable. For example, blends of two or more
polyesters may also be used, with polyester blends which have poly
(ethylene terephthalate) being preferred.
EXAMPLES
The following examples and comparative examples are presented to
illustrate the invention, but the invention should not be limited
by these examples. All parts and percentages are by weight unless
otherwise indicated. The following abbreviations are employed in
the examples:
Bd=butadiene
S=styrene
HEMA=hydroxy ethyl methacrylate
DVB=divinyl benzene.
Apparatus and General Procedure
Modifier compositions are melt blended with APET (Shell 8387) using
a twin screw extruder. The clear amorphous strands are pelletized
and the accumulated product recrystallized before re-extrusion into
0.0762 cm thick sheet. This sheet is then evaluated for impact
strength at 23.degree. C. using the Dynatup impact test
(ASTM-D3763-93). The test is repeated on sheet test samples that
have heat aged at 60.degree. C. over a period of ten days to
establish the relative retention of impact strength of the modified
APET sheet.
Sheet samples are tested for light transmission and haze according
to ASTM-D-1003.
The blue/yellow hue of the sheet samples are measured two ways.
First, the "b" value of the Hunter L,a,b scale is measured. The
Hunter b value is a measure yellowness-blueness, and the procedure
for determining this value is provided in Instruction Manual:
HUNTERLAB TRISTIMULUS COLORIMETER MODEL D25P-9 (rev. A). The second
parameter measured is referred to as the Scattered Yellowness
Index. The Scattered Yellowness Index is calculated according to
the Yellowness Index procedure of ASTM-D-1925, using diffused
(scattered) Transmission values instead of total Transmission
values.
Example 1
A modifier based upon Example 12 of U.S. Pat. No. 5,321,056, with
minor modifications, was prepared according to the following
procedure:
Charge 34.666 parts deionized water and 0.109 parts acetic acid to
a stainless steel reactor capable of withstanding 200 psi (1.38
mPa) pressure. Begin stirring at 100 rpm and heating to 95.degree.
C. while sparging with nitrogen for 30 minutes. At 95.degree. C.,
turn off sparge and add 3.182 parts (33% solids) of a Bd/S (at a
ratio of approximately 70:30) seed emulsion. Also add 2.016 parts
of a 5% aqueous solution of sodium formaldehyde sulfoxylate, then
rinse both with about 2.092 parts deionized water. Evacuate the
reactor to 260 mm Hg. At 95.degree. C., begin feeding butadiene
[12.824 parts]., a mix of monomers [12.121 parts S and 0.252 parts
DVB with a deionized water rinse of 1.356 parts], Dowfax 2A1 soap
solution [3.528 parts at 10% solids] to the reactor over a 5 hour
period . The 2% aqueous t-butyl hydroperoxide solution [4.143
parts] is added over 7.25 hours. The soap and tBHP solutions are
uniform constant rate feeds. The monomer mix and Bd feeds change
each hour as follows:
First hour=0.00076 parts/minute S/DVB and 0.00008 parts/minute
Bd
Second hour=00055 parts/minute S/DVB and 0.00029 parts/minute
Bd
Third hour=00042 parts/minute S/DVB and 0.00042 parts/minute Bd
Fourth hour=00025 parts/minute S/DVB and 0.00059 parts/minute
Bd
Fifth hour=00008 parts/minute S/DVB and 0.00076 parts/minute Bd
Continue the 2% aqueous t-butyl hydroperoxide solution feed after
the monomer feeds and rinse are done. When all feeds are finished,
hold 0.5 hours at 95.degree. C. Cool the reactor to 62.degree. C.
and vent to atmospheric pressure.
The shell is prepared by adding 0.657 parts of a 5% solution of
sodium formaldehyde sulfoxylate to the reactor [rinse with 0.562
parts deionized water]. At 60.degree. C., begin feeding a mix of S
[16.071 parts] and HEMA [2.169 parts] for 1.5 hour at a constant
rate. Also begin feeding 1.369 parts of a 2% solution of t-butyl
hydroperoxide for 1.5 hour at constant rate. After the 1.5 hour
feed is in and rinse [1.264 parts deionized water] is added, chase
with 2% solution of t-butyl hydroperoxide solution [1.094 parts]
for four hours at constant rate, and 4 shots of a 5% solution of
sodium formaldehyde sulfoxylate [0.525 parts total; 0.1313 parts
per shot at 0, 1, 2 and 3 hours]. Add 0.575 parts sodium hydroxide
solution [0.2% solid] and then add a 50% solids emulsion of Irganox
245 [0.180 parts], tris nonyl phenyl phosphite [0.180 parts] and
dilauryl thiodipropionate [0.540 parts]. Cool the batch to
40.degree. C.
The RI of the resulting modifier composition was measured to
1.565.+-.0.002, using ASTM-D-542.
Example 2
A composition within the scope of the present invention was made
according to the following procedure:
Charge 23.319 parts deionized water to a stainless steel reactor
capable of withstanding 200 psi (1.38 mPa) pressure. Add 1.182
parts of a 5% aqueous solution of sodium formaldehyde sulfoxylate.
Begin stirring at 130 rpm and heating to 85.degree. C. while
sparging with nitrogen (0.283 scmh) for 30 minutes. At 85.degree.
C., turn off sparge and add 3.590 parts (33% solids) of a Bd/S (at
a ratio of approximately 70:30) seed emulsion, rinse with about
0.507 parts deionized water. Evacuate the reactor to 362-414 mm Hg.
Begin feeding an emulsified mix of monomers, soap and water to the
reactor over a 4.75 hour period. The emulsified monomer mix
contains: 14.221 parts S, 0.269 parts DVB, 0.213 parts sodium
dodecyl benzene sulfonate soap, 6.606 parts deionized water [and
1.014 parts deionized water rinse]. Feed rates for the emulsified
monomer mix change over time: 1.75 hours at 0.1349 parts/minute,
1.25 hours at 0.0766 parts/minute and 1.5 hours at 0.0152
parts/minute. Other feeds are started the same time as the
emulsified monomer mix: Bd [12.368 parts] is fed over time starting
at 1.75 hours after the start of the emulsified monomers [1.25
hours at 0.0522 parts/minute then 1.5 hours at 0.0938
parts/minute]; 2.377 parts of a 10% aqueous solution of sodium
dodecyl benzene sulfonate solution is fed at a constant rate of
0.0088 parts/minute for 4.5 hours; 1.774 parts of a 5% aqueous
t-butyl hydroperoxide- solution is added at a constant rate of
0.00657 parts/minute for 4.5 hours. At the end of feeds, rinse with
1.267 parts deionized water.
After rinse is added, charge 0.625 parts of a 5% solution of sodium
formaldehyde sulfoxylate to the reactor. Begin feeding an
emulsified styrene charge for 2 hours at 0.1373 parts/minute
[contains: 11.660 parts S, 0.153 parts sodium dodecyl benzene
sulfonate, 0.035 parts t-butyl hydroperoxide, 4.628 parts deionized
water (and 0.760 parts rinse of deionized water)].
After rinse is added, charge 0.070 parts of 5% solution of t-butyl
hydroperoxide and 0.070 parts of 5% solution of sodium formaldehyde
sulfoxylate to the reactor. Hold for 1 hour. Vent the reactor to
atmospheric pressure.
Begin a constant rate feed of emulsified monomers for 1 hour: 6.142
parts S, 0.840 parts HEMA, 0.014 parts DVB, 0.021 parts t-butyl
hydroperoxide, 0.101 parts sodium dodecyl benzene sulfonate, 3.191
parts deionized water (rinse with 0.507 parts deionized water).
Feed shots of 5% solution of t-butyl hydroperoxide [1.460 parts]
and 5% solution of sodium formaldehyde sulfoxylate [1.016 parts]
over 6 hours. A 50% solids emulsion of Irganox 1010 [0.098 parts],
Irganox 245 [0.098 parts] and dilauryl thiodipropionate [0.504
parts] is then added. Cool the batch to 60.degree. C.
The RI of the resulting modifier composition was measured to
1.570.+-.0.002, using ASTM-D-542.
Example 3
Charge 21.794 parts deionized water to a stainless steel reactor
capable of withstanding 200 psi (1.38 mPa) pressure. Add 1.411
parts of a 5% aqueous solution of sodium formaldehyde sulfoxylate.
Begin stirring at 175 rpm and heating to 85.degree. C. while
sparging with nitrogen for 30 minutes . At 85.degree. C., turn off
sparge and add 3.934 parts (35% solids) of a Bd/S (at a ratio of
approximately 70:30) seed emulsion, rinse with about 0.519 parts
deionized water. Evacuate the reactor to 362-414 mm Hg. Begin
feeding an emulsified mix of monomers, soap and water to the
reactor over a 5 hour period. The emulsified monomer mix contains:
23.335 parts S, 0.321 parts DVB, 1.738 parts Dowfax 2A1 soap [20%
solid], 9.392 parts deionized water. Feed rates for the emulsified
monomer mix change over time: 2 hours at 0.1512 parts/minute, 1.5
hour at 0.0338 parts/minute and 1.5 hours at 0.1512 parts/minute.
Other feeds are started as follows: Bd [8.422 parts] is added in a
shot plus a feed--at 1 hour after the start of the emulsified
monomers a shot of 0.804 parts is added, then a 1.5 hour feed at
0.0846 parts/minute is started at 2 hours after the start of the
emulsified monomers; 1.847 parts of a 20% aqueous solution of
Dowfax 2A1 soap is fed at a constant rate of 0.00616 parts/minute
for 5 hours; 2.117 parts of a 5% aqueous t-butyl hydroperoxide
solution is added at a constant rate of 0.00504 parts/minute for 7
hours. At the end of monomer feeds, rinse with 1.038 parts
deionized water. Continue feeding 5% aqueous t-butyl
hydroperoxide-solution for 2 hours. Hold 30 minutes. Pressure
should be about 1.6-1.8.times.10.sup.5 Pa. Vent to atmospheric
pressure.
Charge 0.311 parts of a 5% solution of sodium formaldehyde
sulfoxylate to the reactor. Begin feeding an emulsified styrene mix
for 1 hour at 0.179 parts/minute [contains: 7.161 parts S, 0.527
parts Dowfax 2A1 soap, 3.051 parts deionized water (and 0.519 parts
rinse of deionized water)]. Also feed 0.435 of a 5% solution of
t-butyl hydroperoxide for one hour at 0.00725 parts/minute.
After 1 hour feed is in and rinse is added, begin a constant rate
feed of emulsified monomers for 1 hour [6.287 parts S, 0.859 parts
HEMA, 0.015 parts DVB, 0.527 parts Dowfax 2A1 soap [20% solids],
3.051 parts deionized water] (rinse with 0.519 parts deionized
water)] and also a 1 hour constant rate feed of 0.435 parts of a 5%
solution of t-butyl hydroperoxide solution. After the feeds are in,
feed 0.435 parts of 5% solution of t-butyl hydroperoxide solution
for one hour at constant rate. A 50% solids emulsion of Irganox
1010 [0.100 parts], Irganox 245 [0.100 parts] and dilauryl
thiodipropionate [0.516 parts] is then added. Cool the batch to
60.degree. C.
The RI of the resulting modifier composition was measured to be
1.577.+-.0.002, using ASTM-D-542.
TABLE 1 ______________________________________ Modifier Modifier
Dynatup Impact Strength (J/m .times. 10.sup.2) Example Content Time
in Oven at 60.degree. C. (days) No. (%) 0 1 3 5 10
______________________________________ control 0 246 80.1 81.1 37.9
49.1 1 5 353 280 278 289 323 2 5 257 251 268 247 258 3 5 263 185
185 146 116 1 10 428 307 356 324 381 2 10 369 288 308 290 289 3 10
337 282 193 223 168 ______________________________________
Table 1 reports the measured impact strength of APET blends
containing the modifiers of Examples 1 through 3, compared to the
impact strength of a control sample (i.e., Shell 8387 APET resin
without the addition of modifier). The results illustrate that
compositions within the scope of the present invention, such as the
modifiers of Examples 2 and 3, provide the excellent impact
resistance of compositions reported in U.S. Pat. No. 5,321,056.
TABLE 2 ______________________________________ Modifier Modifier
Scattered Example Concentration % % Yellowness No. (%) Transmission
Haze b Index ______________________________________ control 0 89.5
0.8 0.8 -21 1 5 87.2 2.6 4.6 -226 2 5 88.5 2.8 3.1 -197 3 5 87.8 3
1.8 2 1 10 87.2 3.3 4.2 -224 2 10 88.9 4 2.3 -178 3 10 88.2 3.6 1.6
-17 ______________________________________
Table 2 reports the measured optical properties of APET blends
containing the modifiers of Examples 1 through 3, compared to the
optical properties of the control sample. The results illustrate
that compositions within the scope of the present invention, such
as the modifiers of Examples 2 and 3, provide dramatically improved
optical properties over the compositions reported in U.S. Pat. No.
5,321,056.
* * * * *